Current sources may be implemented in various electrical systems such as, for example, electrical torque motor systems, to drive one or more mechanical systems. Sensing circuits may be used to determine an amount of current that is output from the current source. Conventional sensing circuits typically include a sensing element having a first terminal connect to a high voltage rail of the sensing circuit and a second terminal connected to the low voltage of the sensing circuit. The sensing element measures an electrical voltage generated thereacross in response to receiving the electrical current output from the current source. The measured electrical voltage is then output to an analog-to-digital (A/D) converter configured to calculate a voltage differential between the high voltage rail and the low voltage rail and determine the amount of current output from the current source.
One or more operational amplifiers (op-amps) are typically disposed upstream from the A/D converter to isolate and amplify the voltage differential. The op-amps are powered leveraging current provided by the same power source that powers the current source. When the current source experiences an open circuit, e.g., a disconnection between the current source and a load, the current source outputs a max voltage with no current.
It is common for the op-amps to include variations in performance tolerances such as, for example, maximum voltage swing and/or voltage offset. Consequently, a first op-amp connected to the high voltage rail may output a different voltage level than a second op-amp connected to the low-side rail, even though the op-amps are operating at maximum output. As a result there is a chance (e.g., 50% chance) that the high voltage rail op-amp outputs a higher voltage level than the output of the low voltage rail op-amp causing the voltage differential signal to be positive. This positive differential voltage is sent through an instrumentation amplifier and outputs a positive voltage which is read by the A D converter. The positive voltage A/D reading equates to a positive current measurement, even though there is no current being output from the current source due to the open circuit.